Teacher2Teacher Q&A #19812

Teachers' Lounge Discussion: Explaining concept -x=2 is equal to x=-2

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From: Robert

To: Teacher2Teacher Public Discussion
Date: 2009090413:47:16
Subject: -x=2 is same as x=-2

To explain this can be a real challenge. It results from a basic property of numbers named "Opposite of Opposites," where -(-a)=a and may be visualized when a and negative a are plotted on a one dimensional number line.It is clear that minus a negative a leaves a.Consider the following metaphor.Let x= 2 buckets of cement that must be be lugged up several flights of stairs by Moe accompanied by his friend Joe.Moe soon tires and passes the hod to his friend. Moe is now minus x= 2 buckets of cement.When Joe tires he passes the hod back to Moe.Moe now has +x=2 buckets of cement, while Joe is minus 2 buckets. Except for the transfer (transformation?) nothing has changed as the hod still contains two buckets of cement. We ignore the translation of position. I hope this helps. Robert.

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